Add class composition example

tshemsedinov · tshemsedinov · commit e75389b81dbd · 2018-04-11T23:38:42.000+03:00
diff --git a/JavaScript/4-lambda.js b/JavaScript/4-lambda.js
@@ -0,0 +1,70 @@
+'use strict';
+
+class Rect {
+  constructor(x, y, width, height) {
+    this.x = x;
+    this.y = y;
+    this.width = width;
+    this.height = height;
+  }
+}
+
+const equilateral = Category => class extends Category {
+  constructor(x, y, side) {
+    super(x, y, side, side);
+  }
+};
+
+const serializable = Category => class extends Category {
+  toString() {
+    return `[${this.x}, ${this.y}, ${this.width}, ${this.height}]`;
+  }
+};
+
+const measurable = Category => class extends Category {
+  area() {
+    return this.width * this.height;
+  }
+};
+
+const movable = Category => class extends Category {
+  move(x, y) {
+    this.x += x;
+    this.y += y;
+  }
+};
+
+const scalable = Category => class extends Category {
+  scale(k) {
+    const x = this.width * k / 2;
+    const y = this.height * k / 2;
+    this.width += x;
+    this.height += y;
+    this.x -= x;
+    this.y -= y;
+  }
+};
+
+// Utils
+
+const compose = (...fns) => arg => (
+  fns.reduce((arg, fn) => fn(arg), arg)
+);
+
+// Usage
+
+const Square1 = equilateral(serializable(measurable(
+  movable(scalable(Rect))
+)));
+
+const toSquare = compose(
+  equilateral, serializable, measurable, movable, scalable
+);
+
+const Square2 = toSquare(Rect);
+
+const p1 = new Square2(10, 20, 50);
+p1.scale(1.2);
+p1.move(-10, 5);
+console.log(p1.toString());
+console.log('Area:', p1.area());
